PI Medical (PIM) and the University of Washington (UW) propose jointly to design, fabricate, and test a new, unique multi-electrode array for cochlear implants. The array is designed to be implanted in the scalae tympani of profoundly deaf human patients. Improved function of the array will be achieved with the novel design and fabrication techniques pioneered by PIM, the research experience of the team at UW, and the joint experience of both organizations during Phase I of this STTR project. The collaboration of PIM and UW should provide the medical community with substantially improved functionality of the electrode array at a significantly lower cost than that of today's arrays. Utilizing the data we have obtained on the anatomical geometry of the cochlea, we will place electrodes in optimal locations near neural elements in the apical speech regions of the scala tympani. We have demonstrated that electrode counts can be increased by at least a factor of two over the 22 channels produced and used today. Our experience in Phase I indicates that the proposed geometry will permit finely-focused stimulation of auditory nerve cells. We will test that hypothesis in vitro, in guinea pigs and in nonhuman primates. Our present work indicates that with further development, micro machined electrodes will have improved reproducibility and lower cost than present arrays. We propose to validate those claims by manufacturing several arrays and testing their mechanical and electrical properties in vitro and in vivo. We expect that profoundly deaf patients with remaining VIII nerve cells, who use this novel array, will have improved speech discrimination over those patients who use existing devices. PROPOSED COMMERCIAL APPLICATION: Presently, about 12,000 people wear cochlear implants. The expected economy and versatility of this array should extend the application to at least twice as many people. The recent recommendation that cochlear implants be provided to severely as well as to profoundly deaf subjects will increase the potential market. That recommendation makes this a particularly opportune time for new cochlear implant arrays.